Disk files for information storage generally comprise a stack of disks mounted for rotation with a rotatable hub/spindle combination. Information is written on or read from the disks by means of a number of transducer heads which are movable to different radial positions over the disk surfaces by means of an actuator on which they are mounted.
One very common form of construction is for both actuator and disk stack spindle to be mounted on a rigid base plate beneath the stack. The spindle is normally mounted for rotation in two bearings located in the base plate through which it protrudes to permit connection to an external drive motor. Such an external drive motor may be directly attached to the spindle or may be coupled by way of a belt to an external pulley attached to the spindle. Above the base plate, the spindle supports the disk stack in cantilever fashion within a sealed head/disk enclosure. A disk file typical of this type of construction is shown in U.S. Pat. No. 4,054,931.
One problem with such a construction is that bending or vibration of the base plate or the cantilevered portion of the spindle, produced by thermal gradients or vibration sources such as the actuator and drive motor, can cause severe problems of head to track misregistration or of head to head registration. Although head to track misregistration which is identical for each head can be accommodated by a relatively simple servo system, any non-identical misregistration effects can only be handled by sophisticated servo systems employing position reference information, for example in sectors, on each disk surface. In either case, excessive need for servo correction of head position degrades performance while increasing costs.
Alternative file structures have reduced these effects by increasing the rigidity and symmetry of the disk stack support structure by replacing one-sided base plates by frame or clam-shell structures in which the spindle is supported for rotation in bearings at both ends of the disk stack. Typical of these, are the files described in British Patent GB 2005454B, U.S. Pat. Nos. 4,285,018, and 4,562,499.
While undoubtedly achieving reductions in thermal and vibration induced misregistration, the fact that these files still require the spindle to protrude through that side of the support structure from which it is to be driven introduces some unbalance into the system. Protruding spindles and external drive means also create a potential source of contamination and add to the overall bulk of the file. Such disk files have also required more parts and been more difficult to assemble than the conventional base plate type of file.
The files described in these three references are all high capacity, physically large machines, usually intended to be mounted in stand-alone cabinets. When the problems of designing small files suitable for use in desk-top equipment in an office environment are considered, many of these designs, even scaled down, are found to be relatively wasteful of space.
To save space, the use of a so-called "in-hub" motor has been proposed in the art. One disk file, known as the "Maxtor XT-1000", employing such a motor is described in the journal "Computer Systems" (November 1983 pages 81-84). In this file a rotor within the hub of the rotating disk assembly surrounds a stator mounted on a central stationary spindle. Thus, the spindle drive is centrally located in otherwise wasted space. The overall volume of the file is reduced and a potential source of imbalance and contamination is avoided. However, the Maxtor file employs a traditional base plate which supports the motor, the stack of disks and also a swing-arm actuator from beneath. The construction is therefore susceptible to thermal and vibrational misregistration, particularly as the spindle is unsupported at its end remote from the base plate.
The Maxtor file is not the first instance in which an in-hub motor built around a stationary spindle has been proposed. A much earlier proposal may be found in U.S. Pat. No. 4,005,490. In this case, a file having such a motor also employs a high degree of symmetry in its construction. A rotating hub and single disk are supported for rotation by bearings at opposite ends of a stationary spindle. The spindle is supported by two bridge plates above and below the disk which are attached to a rugged cylindrical frame forming a wall around the periphery of the disk. Each bridge plate also supports a set of fixed heads as the file has no moving heads or actuators. The design has advantages of ruggedness, compactness and symmetry but is of inherently low capacity and high cost because of its single disk and very large number of heads.
Another more recent disk file employing an internal motor is described in published European patent application 0151260. This device is a multi-disk file with a swinging arm actuator both supported in one half of a monocoque (shell) die cast assembly. The other half of the shell assembly seals the head/disk assembly. The internal motor is a brushless DC motor embedded in the spindle hub. However, the spindle itself rotates and protrudes from the sealed HDA where it may be acted on by a spindle brake. The internal structure and bearing arrangement of the motor, hub and spindle is clearly not symmetrical. In particular, the stator of the motor is supported from one side only of the shell so that heat from the stator will be conducted preferentially to one side rather than the other of the structure. Thus the thermal design is highly asymmetrical.
The prior art, therefore, does not show a multi-disk moving head file with an in-hub motor having a stationary spindle as part of a frame structure so as to minimize the effects of thermal and vibration induced misregistration and which uses minimum numbers of parts and material and which is relatively easy to assemble.